Open Radar

 
Summary:

setitimer with ITIMER_VIRTUAL has no effect on 64-bit kernel Mac OS X
10.6.7. ITIMER_REAL works.

Steps to Reproduce:

See attached program.

Expected Results:

expect SIGVTALRM to happen, i.e. V is written by test program until
interrupted by CTRL+C.

Transcript from a machine (with 32-bit kernel) where it works as it
should (real user name replaced with xxx):

sekretariat:~ xxx$ gcc -version
i686-apple-darwin10-gcc-4.2.1: no input files
sekretariat:~ xxx$ gcc -Wall -Werror timer.c -o timer && ./timer
VVVVVVVVVVVVVVVVVVVVVVVVV^C
sekretariat:~ xxx$ uname -a
Darwin sekretariat.local 10.7.0 Darwin Kernel Version 10.7.0: Sat Jan 29 15:17:16 PST 2011; root:xnu-1504.9.37~1/RELEASE_I386 i386
sekretariat:~ xxx$ date
Tue Apr 19 16:29:09 CEST 2011

Actual Results:
SIGVTALRM is never signalled, i.e. V is never written

Transcript from failing machine (with 64-bit kernel):
balrog:PrologTestFiles xxx$ gcc --version
i686-apple-darwin10-gcc-4.2.1 (GCC) 4.2.1 (Apple Inc. build 5664)
Copyright (C) 2007 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

balrog:PrologTestFiles xxx$ gcc -Wall -Werror timer.c -o timer && ./timer
^C
balrog:PrologTestFiles xxx$ uname -a
Darwin balrog.local 10.7.0 Darwin Kernel Version 10.7.0: Sat Jan 29 15:16:10 PST 2011; root:xnu-1504.9.37~1/RELEASE_X86_64 x86_64
balrog:PrologTestFiles xxx$ date
Di 19 Apr 2011 15:39:53 CEST

Regression:

This seems to work with 32-bit kernels. Running on a VMWare guest (Mac
OS X Server 10.6.7) I can reproduce the problem when it boots with
64-bit kernel but the problem goes away when I reboot the same VMWare
guest with a 32-bit kernel (even without recompiling the timer
executable). Note that the above systems refer to real machines, not
VMWare guests.

Notes:

This is a serious bug for us, even though there is a workaround (use 32-bit kernels), since our product (a programming language runtime) is embedded in our customers products and we have no way of informing the end users of the workaround.

/* timer.c BEGIN */
/*

This program demonstrates a bug where setitimer ITIMER_VIRTUAL does
not seem to have any effect (seen on Mac OS X 10.6.7).

[PM] Slightly modified from a program found on the net, originally
written by Marc Feeley.

Compile and run as

 gcc -Wall -Werror timer.c -o timer && ./timer

it should write one V on stdout every 1/10 of a second.

or

 gcc -DITIMER_SECS=1 timer.c -o timer && ./timer

it should write one V on stdout about once every second.

When the bug occurs the program just hangs.

The program can be built to use ITIMER_REAL instead, with

 gcc -DUSE_ITIMER_REAL timer.c -o timer && ./timer

this has not been seen to hang.

*/

#include <sys/time.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>

#ifndef ITIMER_SECS
#define ITIMER_SECS 0
#endif
#ifndef ITIMER_USECS
#define ITIMER_USECS 100000
#endif  /* ITIMER_USECS */

#define CHECK(EXPR) do{                         \
   if ((EXPR) == -1) {                         \
     int e = errno;                            \
     fprintf(stderr, "%s:%d ERROR errno=%d\n", \
             __FILE__, (int)__LINE__, e);      \
     fflush(stderr);                           \
     abort();                                  \
   }                                           \
 } while (0)

void heartbeat_interrupt_handler (int sig)
{
#ifdef USE_ITIMER_REAL
write (STDOUT_FILENO, "R", 1);
#else
write (STDOUT_FILENO, "V", 1);
#endif
}

int main (int argc, char *argv[])
{
struct itimerval tv;
int secs = ITIMER_SECS;
int usecs = ITIMER_USECS;

#ifdef USE_ITIMER_REAL
int HEARTBEAT_ITIMER = ITIMER_REAL;
int SIG = SIGALRM;
#else
int HEARTBEAT_ITIMER = ITIMER_VIRTUAL;
int SIG = SIGVTALRM;
#endif

struct sigaction act;
act.sa_handler = heartbeat_interrupt_handler;
act.sa_flags = 0;
CHECK(sigemptyset(&act.sa_mask));
CHECK(sigaction(SIG, &act, 0));

tv.it_interval.tv_sec  = secs;
tv.it_interval.tv_usec = usecs;
tv.it_value.tv_sec     = secs;
tv.it_value.tv_usec    = usecs;
CHECK(setitimer(HEARTBEAT_ITIMER, &tv, 0));

for (;;)
  {
    /* keep CPU 100% busy */
  }

return 0;
}

/* timer.c END */